This invention relates to a catalyst for use in the manufacture of unsaturated esters, particularly diacyloxyalkenes. More particularly, it is concerned with a solid catalyst for use in the manufacture of diacyloxyalkenes by reacting conjugated dienes, carboxylic acids and oxygen.
Diacyloxyalkenes are useful as raw materials for a variety of industrial applications. For example, 1,4-butanediol derived from 1,4-diacyloxybutene-2 is an industrially useful compound serving as a solvent, or an intermediate for the manufacture of tetrahydrofuran, .gamma.-butyrolactone, polyesters, or the like.
It is known to manufacture diacyloxyalkenes by contacting a conjugated diene and oxygen with a catalyst composed of a Group VIII noble metal such as palladium and platinum, or a mixture of such a noble metal with selenium, tellurium, anitmony, bismuth, lead or the like in the presence of a carboxylic acid. For example, it has hitherto been proposed to manufacture 1,4-diacyloxy-2-butenes by contacting a conjugated diene, oxygen and a carboxylic acid with a catalyst composed of palladium, iridium, platinum, rhodium, ruthenium or the like, or a mixture of such a metal with copper, silver, zinc, nickel or the like as disclosed in Japanese Patent Publication No. 27290/1973, or to use a catalyst composed of a combination of palladium, and antimony, bismuth, selenium or tellurium as disclosed in Japanese Patent Application Laid-Open Specification No. 11812/1974.
Applicants have now found that the catalysts prepared by known methods do not have a sufficiently high activity because the metal component is not uniformly distributed on the carrier, and also because known multicomponent catalysts containing a plurality of metal components do not have a uniform distribution of each component on the carrier. Examples of such known catalysts include a catalyst obtained by dissolving a noble metal salt such as palladium chloride, and a salt of copper, zinc or the like in a mineral acid or acetic acid, incorporating a carrier into the resulting solution, and evaporating the mixture to dryness (Japanese Patent Publication No. 27290/1973); a catalyst obtained by treating with nitric acid activated carbon prepared by crushing coconut shells, incorporating the activated carbon into a hydrochloric acid solution containing palladium chloride, tellurium dioxide, selenium dioxide and antimony trichloride, and evaporating the solution to dryness (Japanese Patent Application Laid-Open Specification No. 11812/1974); a catalyst obtained by incorporating coconut shell activated carbon into an acetone solution of sulfur chloride, evaporating it to dryness, incorporating the evaporation product into an aqueous solution of hydrochloric acid containing palladium and niobium pentachloride, and evaporating the solution to dryness (Japanese Patent Application Laid-Open Specification No. 14914/1979), and a catalyst obtained by incorporating an ethanol solution of palladium acetate and activated carbon into a nitric acid solution of copper, and evaporating the mixed solution to dryness (Japanese Patent Application Laid-Open Specification No. 147189/1979).
All the known methods for preparing a catalyst by incorporating a carrier into a solution containing a catalytic component involve difficulty in achieving even distribution of the catalytic component from the surface of the catalyst to the interior thereof, and have a tendency to contain a smaller quantity of the catalytic component in the interior thereof. With a known catalyst containing a plurality of catalytic components, there is difficulty in maintaining the optimum proportions of the components throughout it, and different quantities of each component are contained in different parts thereof.
Applicants have therefore investigated a method which permits uniform distribution of the catalytic component or components on the carrier, and have discovered that it is possible to achieve uniform distribution of the or each catalytic component on the carrier if one uses a two-step impregnation method. That is to say, a noble metal belonging to Group VIII of the periodic table is supported on the carrier using a solution prepared by dissolving the metal compound in a mixture of an organic solvent and a mineral acid, and after washing, drying and calcining as may be needed, a compound of an element belonging to Group IV, V, or VI of the periodic table is supported on the obtained carrier containing the noble metal, using an organic solvent solution of the compound. This invention is based on this dicovery.